The present invention relates to low heat output composites and composites exhibiting low flammability, particularly those composites used in applications where it is desired that the composite exhibit a low heat release rate and low total heat release when subjected to combustion conditions including a radiant heat source. Exemplary of such applications are structural panels and laminates used in the interior of airplanes.
The flammability of airline cabin interior materials used in commercial transport aircraft is governed by regulations issued by the Federal Aviation Administratiton (FAA). The FAA requires that all interior materials must be "selfextinguishing" when held in a vertical orientation and subjected to a flame along the bottom edge. It is generally accepted that this vertical flame test addresses the ignitability of a material exposed to a small ignition source (e.g., a condition that might accidentally occur while an aircraft is in flight). Over the past twenty years, for United States air carriers, there has not been a fatal in-flight fire originating in an accessible area of a passenger airplane. Undoubtedly, the selfextinguishing requirements issued by the FAA have contributed to this excellent record. A small number of fire fatalities that do occur in accidents involving U.S. air carriers are the result of post-crash fires, that are often initiated by a large pool of burning aviation fuel.
Airline cabin fire hazards effecting survivability are: flammability of materials, heat release of materials, smoke and toxicity. The relative importance of each of these hazards will depend on the circumstances surrounding any particular accident. For a post-crash cabin fire, a large fuel fire is the most predominant type of ignition source. It has been determined that "flash over" has the greatest bearing on occupant survivability. "Flash over" is the sudden and rapid uncontrolled growth of a fire from the area around the ignition source to the remainder of the cabin interior. Before the onset of flash over, the levels of heat, smoke and toxic gas are clearly tolerable; after the onset of flash over, all the hazards increase rapidly to levels that would make survival very unlikely. Thus, for an intense post-crash fire, the most effective and direct means of minimizing the hazards resulting from burning cabin materials is to delay the onset of flash over. Flammability considerations, in contrast to smoke and toxicity considerations, directly effect the occurrence of flash over.
Airline industry concern has been directed to reducing the flammability and ignitability of composite materials used in the construction of airline interior sidewalls, storage bins, ceilings, and partitions. From a fire safety viewpoint, sidewall panels are an important concern because of their large surface area potentially being involved in a cabin fire.
Fiber composite materials used in the airline industry generally include various epoxy compositions that have been used to impregnate the reinforcing system of fibers. The impregnated system of reinforcing fibers exhibits good adhesion so that they may be easily attached to the core material of the composites. However, the epoxy resins when exposed to flames will burn and produce smoke, conditions that are undesirable for obvious safety reasons. It is possible to impart a self-extinguishing/low flammability property to the epoxy resins by halogenating the epoxy resins. Bromine is a particular halogen which is useful in lowering the flammability of an epoxy resin; however, the bromine does nothing to reduce the level of smoke that is produced when the epoxy resin burns. In fact, the bromination of the epoxy resin may lead to increased levels of smoke production.
Fiber reinforced composites have also been provided by impregnating mats of reinforcing fibers with phenolic resins. These phenolic resins will also burn and produce smoke when exposed to combustion conditions. Further, when the phenolic resins are used, various additives are usually included to impart flexibility to the impregnated fiber composite. These additives, such as nylon and rubber, are additional fuel sources that promote the burning and smoking of the fiber composite when subjected to combustion conditions.